1. The Field of the Invention
This invention relates to television receivers and apparatuses adapted to disable such receivers for use on selected channels.
2. Description of the Prior Art
The prior art abounds with scanning radio receivers or search tuning systems each possessing the characteristic of enabling the receivers to select preferred channels at the will of the user. U.S. Pat. No. 3,824,475 issued on July 16, 1974 to P. W. Pflasterer teaches a signal-seeking receiver which automatically scans a plurality of channels of respective predetermined radio frequencies lying in a multiplicity of frequency bands. The channels are tuned in successively by successively coupling respective tuning crystals into the tuning circuit of a signal generator which produces the beating signals for heterodyning. Scanning is stopped upon receiving a signal. For higher bands the frequency of a basic oscillator is multiplied by cascaded frequency-multiplying circuits. Automatic frequency control is provided for channels in the highest band, with gating means for disabling the frequency control in the absence of a received signal. For bypassing selected channels during scanning, the clock driving the scanner is speeded up when the channels to be bypassed would otherwise be tuned in.
U.S. Pat. No. 3,714,580 issued on Jan. 30, 1973 to E. F. Close discloses an electronic tuning system for a heterodyne type receiving device wherein the receiving device consists of a voltage tuned radio frequency amplifier, a voltage tuned local oscillator, a first control circuit having an output which varies as a function of the magnitude of a received signal, and a second control circuit having an output which varies as a function of the frequency of an intermediate frequency signal within the receiver. Electronic search tuning is achieved by providing a first voltage source having an output which varies as a substantially linear function of time, and supplying this output to both the radio frequency amplifier and the local oscillator during the tuning process and switching from the first voltage source to the second control circuit upon finding a sufficiently strong incoming signal.
U.S. Pat. No. 3,714,585 issued on Jan. 30, 1973 to R. C. Koch describes a multi-frequency receiver having a local oscillator with a plurality of channel determining elements sequentially connectable to control the received frequency. A shift register controlled by a multi-speed clock is used in sequencing through the channel elements. Switches are provided for each channel to control the speed of the clock. When a channel switch is set for a high speed, and as the channel determining element associated with that switch is connected to the oscillator circuit, the clock pulses rapidly again thus sequencing the receiver to the next channel determining element before the carrier sensing circuitry can lock on the channel.
All of the aforementioned patterns fail to provide an apparatus which totally precludes selectively one or more channels or a multi-frequency receiver for indefinite periods of time, controllable by a master switch, and economically fabricated so as to be includable and easily added to the circuitry of existing television receivers.